As the substrate processing apparatus, there is a batch type substrate processing apparatus which processes a necessary number of substrates at a time, e.g., a vertical CVD apparatus which has a vertical reaction furnace and which processes a necessary number of substrates at a time.
For producing semiconductor devices, a batch type vertical hot wall decompression CVD apparatus is widely used for forming a CVD film such a polycrystalline silicon film, a silicon nitride film and the like on a substrate (wafer).
A general batch type vertical hot wall decompression CVD apparatus includes a reaction tube comprising an inner tube and an outer tube which is concentric with the inner tube, a heater which is disposed such as to surround the outer tube and which heats the inside of the reaction tube, a gas introducing nozzle through which reaction gas is introduced into the inner tube, and a vertical furnace comprising an exhaust port or the like through which the reaction tube is evacuated. A necessary number of multi-stacked wafers are held in their horizontal postures and in this state, the wafers are brought into the inner tube from below. Reaction gas is introduced into the inner tube through the gas introduction nozzle, and the inside of the reaction tube is heated by the heater, thereby forming CVD films on the wafers.
As such a conventional substrate processing apparatus, there is a vertical CVD apparatus as described in Japanese Patent Application Laid-open No. 2000-68214 for example.
This vertical CVD apparatus includes a plurality of reaction gas supply nozzles as the gas introducing nozzle. A quartz tube having ¼ inch diameter (outer diameter) is used as the reaction gas supply nozzle. Each reaction gas supply nozzle comprises a horizontal portion which is inserted below the inner tube from the horizontal direction, and a vertical portion which extends upward along an inner surface of the inner tube, and the reaction gas supply nozzle is formed into L-shape. The vertical portion is provided in a gap between the inner tube, a boat and a wafer held by the boat. An upper end of the vertical portion is opened. Lengths of vertical portions of the respective reaction gas supply nozzles are different from one another in stages so that reaction gas can be dispersed and supplied into the inner tube.
When a CVD film is to be formed on a wafer, a reaction product is formed not only on the wafer surface, but is also adhered to and deposited on an inner surface of the inner tube 3 or an interior of the reaction gas supply nozzle 106 as shown in FIG. 13. Especially a portion of the reaction gas supply nozzle 106 that is opposed to the heater 5 is heated by the heater 5 and thus, there is a high tendency that the reaction product 47 is adhered to and deposited on this portion of the reaction gas supply nozzle 106. Further, since the pressure in the reaction gas supply nozzle 106 is higher than the pressure outside of the nozzle 106, a reaction product 47 adhered to an inner wall of the nozzle 106 is three to four times thicker than a reaction product adhered to an outer wall of the nozzle 106. For this reason, when a flat polycrystalline silicon film (this will be described later) having about 5,000 to 10,000 Å thickness is to be formed using a quartz tube having ¼ inch diameter (outer diameter) as the nozzle 106, the nozzle 106 is clogged during processing of three to four batches. In this case, cleaning of the nozzle can not be carried out, and the only way is to replace the nozzle 106 with a clean one every three to four times batch processing. Therefore, maintenance operation such as cleaning of the reaction gas supply nozzle must frequently be carried out under the necessity, and this deteriorates the rate of operation and throughput of the substrate processing apparatus.
In view of such circumstances, it is a main object of the present invention to prevent a gas introducing nozzle from being clogged soon even if a thick film such as a thick polycrystalline silicon film is formed, to elongate a maintenance cycle, to reduce downtime of the apparatus, to lighten the maintenance operation, and to enhance the throughput.